Xiaomin Zhong

A functional genomic approach identifies FAL1 as an oncogenic long noncoding RNA that associates with BMI1 and represses p21 expression in cancer.

In a genome-wide survey on somatic copy-number alterations (SCNAs) of long noncoding RNA (lncRNA) in 2,394 tumor specimens from 12 cancer types, we found that about 21.8% of lncRNA genes were located in regions with focal SCNAs. By integrating bioinformatics analyses of lncRNA SCNAs and expression with functional screening assays, we identified an oncogene, focally amplified lncRNA on chromosome 1 (FAL1), whose copy number and expression are correlated with outcomes in ovarian cancer. FAL1 associates with the epigenetic repressor BMI1 and regulates its stability in order to modulate the transcription of a number of genes including CDKN1A. The oncogenic activity of FAL1 is partially attributable to its repression of p21. FAL1-specific siRNAs significantly inhibit tumor growth in vivo.

Identification of MicroRNAs Regulating Reprogramming Factor LIN28 in Embryonic Stem Cells and Cancer Cells

LIN28 (a homologue of the Caenorhabditis elegans lin-28 gene) is an evolutionarily conserved RNA-binding protein and a master regulator controlling the pluripotency of embryonic stem cells. Together with OCT4, SOX2, and NANOG, LIN28 can reprogram somatic cells, producing induced pluripotent stem cells. Expression of LIN28 is highly restricted to embryonic stem cells and developing tissues. In human tumors, LIN28 is up-regulated and functions as an oncogene promoting malignant transformation and tumor progression. However, the mechanisms of transcriptional and post-transcriptional regulation of LIN28 are still largely unknown. To examine microRNAs (miRNAs) that repress LIN28 expression, a combined in silico prediction and miRNA library screening approach was used in the present study. Four miRNAs directly regulating LIN28 (let-7, mir-125, mir-9, and mir-30) were initially identified by this approach and further validated by quantitative RT-PCR, Western blot analysis, and a LIN28 3′-UTR reporter assay. We found that expression levels of these four miRNAs were clustered together and inversely correlated with LIN28 expression during embryonic stem cell differentiation. In addition, the expression of these miRNAs was remarkably lower in LIN28-positive tumor cells compared with LIN28-negative tumor cells. Importantly, we demonstrated that these miRNAs were able to regulate the expression and activity of let-7, mediated by LIN28. Taken together, our studies demonstrate that miRNAs let-7, mir-125, mir-9, and mir-30 directly repress LIN28 expression in embryonic stem and cancer cells. Global down-regulation of these miRNAs may be one of the mechanisms of LIN28 reactivation in human cancers.

Mir-30d Regulates multiple genes in the autophagy pathway and impairs autophagy process in human cancer cells

In human epithelial cancers, the microRNA (miRNA) mir-30d is amplified with high frequency and serves as a critical oncomir by regulating metastasis, apoptosis, proliferation, and differentiation. Autophagy, a degradation pathway for long-lived protein and organelles, regulates the survival and death of many cell types. Increasing evidence suggests that autophagy plays an important function in epithelial tumor initiation and progression. Using a combined bioinformatics approach, gene set enrichment analysis, and miRNA target prediction, we found that mir-30d might regulate multiple genes in the autophagy pathway including BECN1, BNIP3L, ATG12, ATG5, and ATG2. Our further functional experiments demonstrated that the expression of these core proteins in the autophagy pathway was directly suppressed by mir-30d in cancer cells. Finally, we showed that mir-30d regulated the autophagy process by inhibiting autophagosome formation and LC3B-I conversion to LC3B-II. Taken together, our results provide evidence that the oncomir mir-30d impairs the autophagy process by targeting multiple genes in the autophagy pathway. This result will contribute to understanding the molecular mechanism of mir-30d in tumorigenesis and developing novel cancer therapy strategy.

A Combined Array-Based Comparative Genomic Hybridization and Functional Library Screening Approach Identifies mir-30d As an Oncomir in Cancer

Oncomirs are microRNAs (miRNA) that acts as oncogenes or tumor suppressor genes. Efficient identification of oncomirs remains a challenge. Here we report a novel, clinically guided genetic screening approach for the identification of oncomirs, identifying mir-30d through this strategy. mir-30d regulates tumor cell proliferation, apoptosis, senescence, and migration. The chromosomal locus harboring mir-30d was amplified in more than 30% of multiple types of human solid tumors (n = 1,283). Importantly, higher levels of mir-30d expression were associated significantly with poor clinical outcomes in ovarian cancer patients (n = 330, P = 0.0016). Mechanistic investigations suggested that mir-30d regulates a large number of cancer-associated genes, including the apoptotic caspase CASP3. The guided genetic screening approach validated by this study offers a powerful tool to identify oncomirs that may have utility as biomarkers or targets for drug development.

Lin-28 Homologue A (LIN28A) Promotes Cell Cycle Progression via Regulation of Cyclin-dependent Kinase 2 (CDK2), Cyclin D1 (CCND1), and Cell Division Cycle 25 Homolog A (CDC25A) Expression in Cancer

Background: LIN28A may function as a critical oncogene in human cancer. Results: LIN28A controls expression of numerous cell cycle regulatory genes, including CDK2, CCND1, and CDC25A, in cancer. Conclusion: LIN28A promotes cell cycle progression in cancer mediated by both let-7-dependent and -independent mechanisms. Significance: Our data shed new light on how LIN28A regulates cell cycle in cancer. The RNA-binding protein LIN28A regulates the translation and stability of a large number of mRNAs as well as the biogenesis of certain miRNAs in embryonic stem cells and developing tissues. Increasing evidence indicates that LIN28A functions as an oncogene promoting cancer cell growth. However, little is known about its molecular mechanism of cell cycle regulation in cancer. Using tissue microarrays, we found that strong LIN28A expression was reactivated in about 10% (7.1–17.1%) of epithelial tumors (six tumor types, n = 369). Both in vitro and in vivo experiments demonstrate that LIN28A promotes cell cycle progression in cancer cells. Genome-wide RNA-IP-chip experiments indicate that LIN28A binds to thousands of mRNAs, including a large group of cell cycle regulatory mRNAs in cancer and embryonic stem cells. Furthermore, the ability of LIN28A to stimulate translation of LIN28A-binding mRNAs, such as CDK2, was validated in vitro and in vivo. Finally, using a combined gene expression microarray and bioinformatics approach, we found that LIN28A also regulates CCND1 and CDC25A expression and that this is mediated by inhibiting the biogenesis of let-7 miRNA. Taken together, these results demonstrate that LIN28A is reactivated in about 10% of epithelial tumors and promotes cell cycle progression by regulation of both mRNA translation (let-7-independent) and miRNA biogenesis (let-7-dependent).

miRNAs in Human Cancer

MicroRNAs (miRNAs) are small (∼18-25 nucleotides), endogenous, noncoding RNAs that regulate gene expression in a sequence-specific manner via the degradation of target mRNAs or the inhibition of protein translation. miRNAs are predicted to target up to one-third of all human mRNAs. Each miRNA can target hundreds of transcripts and proteins directly or indirectly, and more than one miRNA can converge on a single target transcript; thus, the potential regulatory circuitry afforded by miRNAs is enormous. Increasing evidence is revealing that the expression of miRNAs is deregulated in cancer. High-throughput miRNA quantification technologies provide powerful tools to study global miRNA profiles. It has become progressively more apparent that, although the number of miRNAs (∼1,000) is much smaller than the number of protein-coding genes (∼22,000), miRNA expression signatures more accurately reflect the developmental lineage and tissue origin of human cancers. Large-scale studies in human cancer have further demonstrated that miRNA expression signatures are associated not only with specific tumor subtypes but also with clinical outcomes.

Suppression of MicroRNA 200 Family Expression by Oncogenic KRAS Activation Promotes Cell Survival and Epithelial-Mesenchymal Transition in KRAS-Driven Cancer

ABSTRACT Oncogenic KRAS contributes to malignant transformation, antiapoptosis, and metastasis in multiple human cancers, such as lung, colon, and pancreatic cancers and melanoma. MicroRNAs (miRNAs) are endogenous 18- to 25-nucleotide noncoding small RNAs that regulate gene expression in a sequence-specific manner via the degradation of target mRNAs or inhibition of protein translation. In the present study, using array-based miRNA profiling in IMR90 and MCF10A cells expressing oncogenic KRAS, we identified that the expression of the microRNA 200 (mir-200) family was suppressed by KRAS activation and that this suppression was mediated by the transcription factors JUN and SP1 in addition to ZEB1. Restoration of mir-200 expression compromised KRAS-induced cellular transformation in vitro and tumor formation in vivo. In addition, we found that enforced expression of mir-200 abrogated KRAS-induced resistance to apoptosis by directly targeting the antiapoptotic gene BCL2. Finally, mir-200 was able to antagonize the epithelial-mesenchymal transition (EMT) driven by mutant KRAS. Collectively, our results suggest that repression of endogenous mir-200 expression is one of the important cellular responses to KRAS activation during tumor initiation and progression.

Oncogenic RAS Regulates Long Noncoding RNA Orilnc1 in Human Cancer

RAS and its downstream cascades transmit cellular signals, resulting in increased transcription of genes involved in cell growth and division. Protein-coding gene targets of RAS signaling have been characterized extensively, but long noncoding RNAs (lncRNA) regulated by these processes have not. Using a custom-designed lncRNA microarray, we identified the lncRNA Orilnc1 as a genetic target of RAS that is critical for RAS oncogenicity. Orilnc1 expression was regulated by RAS-RAF-MEK-ERK signaling via the transcription factor AP1. Orilnc1 was highly expressed in BRAF-mutant cancers, such as melanoma. Silencing of Orilnc1 blocked tumor cell proliferation and growth in vitro and in vivo In addition, Orilnc1 blockade reduced expression of cyclin E1 and induced G1-S cell-cycle arrest in tumor cells. Taken together, our results identify Orilnc1 as a novel, nonprotein mediator of RAS/RAF activation that may serve as a therapeutic target in RAS/RAF-driven cancers. Cancer Res; 77(14); 3745-57. ©2017 AACR.

Noncoding RNA for Cancer Gene Therapy

Gene therapy is a prospective strategy to modulate gene expression level in specific cells to treat human inherited diseases, cancers, and acquired disorders. A subset of noncoding RNAs, microRNAs (miRNAs) and small interference RNAs (siRNAs), compose an important class of widely used effectors for gene therapy, especially in cancer treatment. Functioning through the RNA interference (RNAi) mechanism, miRNA and siRNA show potent ability in silencing oncogenic factors for cancer gene therapy. For a better understanding of this field, we reviewed the mechanism and biological function, the principles of design and synthesis, and the delivery strategies of noncoding RNAs with clinical potentials in cancer gene therapy.

RNA-binding protein LIN28B inhibits apoptosis through regulation of the AKT2/FOXO3A/BIM axis in ovarian cancer cells

LIN28B is an evolutionarily conserved RNA-binding protein that regulates mRNA translation and miRNA let-7 maturation in embryonic stem cells and developing tissues. Increasing evidence demonstrates that LIN28B is activated in cancer and serves as a critical oncogene. However, the underlying molecular mechanisms of LIN28B function in tumorigenesis are still largely unknown. Here we report that LIN28B was expressed in over half of the patients with epithelial ovarian cancer who were examined (n = 584). Functional experiments demonstrated that LIN28B inhibited ovarian cancer cell apoptosis. Furthermore, we showed that the proapoptotic factor BIM played an essential role in the antiapoptotic function of LIN28B. RNA-IP microarray analysis suggested that LIN28B binds to mRNAs that are associated with the DNA damage pathway, such as AKT2, in ovarian cancer cells. By binding to AKT2 mRNA and enhancing its protein expression, LIN28B regulated FOXO3A protein phosphorylation and decreased the transcriptional level of BIM, which antagonized the antiapoptosis activity of LIN28B. Taken together, these results mechanistically linked LIN28B and the AKT2/FOXO3A/BIM axis to the apoptosis pathway. The findings may have important implications in the diagnosis and therapeutics of ovarian cancer.Cancer: ovarian cancer oncogene forces cells to stay aliveResearchers in China have uncovered the molecular mechanism behind the activity of a gene related to ovarian cancer. Xiaomin Zhong’s team at Sun Yat-Sen University knocked down the gene, LIN28B, in cancer cell lines and discovered that this increased their response to a chemical, which induces programmed cell death (PCD). By contrast, increasing LIN28B expression reduced PCD sensitivity, leading to the conclusion that LIN28B inhibits PCD in cancer cells. Examining gene expression in the knockdown lines revealed that LIN28B suppresses the activity of the PCD-related gene BIM. Further experiments showed that this happens through the modulation of genes upstream of BIM. These results demonstrate that LIN28B acts by regulating a genetic pathway, which regulates PCD. Altogether, this improved understanding of LIN28B may help with the diagnosis and therapy of ovarian cancer.